In general, light sources used in projection TVs, etc., include projectors such as a compact CRT (Cathode Ray Tube), LCD (Liquid Crystal Display) and DLP (Digital Light Processing). Among those, light sources using compact display technology such as LCD and DLP are referred to as microdisplay (MD) type light sources. Transmission type screens are used for the above devices, wherein such a transmission type screen generally comprises a fresnel sheet and lenticular sheet. The lenticular sheet includes a cylindrical lens array, also referred to as a lenticular lens, on the input surface and/or output surface, and includes a light-absorbing layer disposed on the output surface in order to inhibit the reflection of external light.
To form such light-absorbing layers, printing processes have been generally used in conventional lenticular sheets for CRT screens. However, in the case of screens for MD, it is necessary to form a light-absorbing layer with high precision, because the pitch (width) of a lenticular lens is small to a degree of between several hundreds and several tens micrometers. Therefore, conventional printing processes were not applicable to lenticular sheets for MD. Additionally, in the case of a projection TV using an MD type light source, it is important to provide a sufficient degree of contrast to a screen, because the light source itself has insufficient contrast characteristics. In this regard, it is important to ensure a sufficient area of light-absorbing layer to the total area of the screen, as a primary means for providing sufficient contrast characteristics to the screen.
U.S. Pat. No. 5,870,224 or Japanese Laid-Open Patent No. Sho59-121033 suggests a method for producing a lenticular sheet for MD. In the method, photoresist having adhesive property is coated on the output surface of a lenticular sheet and parallel light is irradiated to the input surface of the lenticular sheet, so that the light collected on the surface of photoresist through an input lens causes the adhesion property of photoresist to be removed at the portions where the light is collected. Then, toner is coated on the surface of photoresist and parts of the toner, where the toner is not attached, are removed so that the toner can be attached only at the portions where the light is not collected, resulting in the formation of a light-absorbing layer. FIG. 7 shows a lenticular sheet 10 obtained by the above-described method. The above-described method has an advantage in that it allows a lenticular sheet 10 having a lenticular lens 13 with a fine pitch (width) to be easily manufactured, because the alignment of the lenticular lens 13 as an input lens and a light-absorbing layer 18 can be accomplished automatically during the manufacture of the lenticular sheet 10.
However, the above-described method has disadvantages that it needs additional processing steps including a step for coating photoresist, a step for irradiating light uniformly, a step for coating toner and a step for removing the toner, etc., thereby increasing the time and cost needed for the manufacture of a lenticular sheet compared to other conventional processes.
Moreover, the lenticular sheet manufactured by the above-described method has problems in that a light-absorbing layer having a sufficient area cannot be obtained, when the light collected on the photoresist layer 16 has aberration or is diffused by a light-diffusing so as to increase the area of a focus. Accordingly, the lenticular sheet should have a structure wherein a light-diffusing layer 12 is formed on the light-absorbing layer 18 (when viewed along the direction facing to a viewer). However, the above-mentioned structure increases the amount of light reflected toward the eyes of a viewer, because external light experiences diffusive reflection by the light-diffusing layer 12 before it is absorbed by the light-absorbing layer 18, and thus show a problem of degradation in contrast characteristics of the whole screen.
Further, when a light-absorbing layer is formed by means of the above-described method, the light-absorbing layer is not formed according to a predetermined design. On the contrary, the position and area of a light-absorbing layer are determined depending on the light collecting characteristics of a lenticular lens, characteristics of the photoresist or those of the light source used in forming the light-absorbing layer. Therefore, even if a designer skilled in the art wants to improve the contrast characteristics by increasing the area of a light-absorbing layer, designs on demand cannot be permitted.